Is there any good method of sharpening these things?
As Leah Bolden from See Jane Drill shows, this is easily done using a tri square file. She shows her technique in this video.
Basically, you use a triangular file to file new teeth. This even works on a blade where they have been ground almost flat. She recommends clamping the blade between two pieces of wood and using those as a depth guide.
Like Leah says,
"you can do this."
Generally, those are disposable items.
Could you sharpen it? I'm sure you could, but your results would probably be less than satisfactory. Getting enough of the teeth sharp enough to notice a difference in cutting, while not bending them too much out of line (you don't want that kerf getting too wide, or if you're using it for a flush cut, a random tooth sticking out scratching up a finish surface), is going to be difficult.
Yes, they can be expensive to buy, but the "Random Brand" blade you have in your hand, made in China, purchased via Amazon, is cheap enough to just toss in the bin once it's dull.
Honestly, I look at that one, though, and think "that's nearly new!". Usually, I find the teeth are nearly gone (even when just cutting wood) before I toss them. Not because I'm that much of a spendthrift, but because they just wear out that fast. Maybe I should try your brand...
Those blades are available to be purchased in quantity for under 67 CENTS each!
Yes you can sharpen them, but why would you spend the time?
There are 2 views on this. One is that it can be done. The other that it is not worth the time.
Perhaps this can be turned into something positive.
How about if the blades were collected, from a number of sources; friends, handymen, contractors etc.
The blades and the tools needed to sharpen them are then given to social organizations that have the people and time to devote to the sharpening process. Places like retirement homes, centers for occupational training for the disabled, even maybe church groups. Any organization that has people with some time and the need to generate some money.
Once sharpened they can be collected and sold at flea markets or other places, with the proceeds to go to that organization.
I would donate all my blades and agree to buy them back at 1.00 per blade, just to benefit the organization.
There have to be thousands if not millions of these blades discarded because sharpening is not feasible.
Perhaps this can be the birth of a new money stream (even if a small one) for some charities and organizations.
I'd use a rotary tool (Dremel) with an abrasive disk. Gently buff each tooth face with the face of the wheel, being careful not to put too much pressure on the wheel. They don't have a lot of strength that direction. Pay attention to angle to retain the original shape.
You might also find a bit with the right shape to sharpen each vee.